About the FL-9 

The EMD FL9 is a model of electro-diesel locomotive, capable of operating either as a traditional diesel-electric locomotive or as an electric locomotive powered from a third rail. Sixty units were built between October 1956 and November 1960 by General Motors Electro-Motive Division for the New York, New Haven and Hartford Railroad (the "New Haven").

Due to concerns about diesel emissions in the East River Tunnels and the underground tracks of Grand Central Terminal and Penn Station, passenger trains entering New York City have long been required to use electrical power. At the same time, much of the New Haven's trackage was not electrified beyond New Haven. To allow passenger trains to travel to New York City from non-electrified lines without requiring a change of locomotives, the New Haven Railroad purchased a class of locomotive that could switch between diesel and electric power on the fly.

EMD's answer was a new locomotive based on their existing FP9, but lengthened to accommodate additional equipment, such as a larger train heating steam boiler and third rail contact shoes. Due to the additional weight, the locomotive was equipped with a three-axle rear truck, giving it an uncommon B-A1A wheel arrangement. 

In 1969, the New Haven FL9 fleet passed to Penn Central upon the merger of the Pennsylvania Railroad and New York Central Railroad, as the ICC required the newly formed company to assume control of the bankrupt New Haven. Some were repainted in Penn Central schemes, while others remained in their former New Haven paint. When the New York Metropolitan Transportation Authority (MTA) began funding these commuter services in 1970, many were repainted blue with a bright yellow nose, although they remained Penn Central-owned. The locomotives passed to Conrail upon its formation in 1976 from the bankrupt PC. Twelve FL9s were sold to Amtrak, six of which were remanufactured by Morrison-Knudsen starting in 1978 and remained in Amtrak service until at least 1996.

In 1983, Conrail passed its commuter operations to state agencies. In New York State, the MTA formed Metro-North Railroad as a subsidiary company to operate these, and operations in Connecticut under contract with that state. The locomotives were repainted in Metro-North colors (more commonly in a silver, blue, and red scheme;[7] some in a silver and blue scheme[8]), and a large number of them, now in some cases over 25 years old, were rebuilt and modernized. Ten rebuilt for the Connecticut Department of Transportation (CDT) were painted in the original New Haven paint scheme in recognition of their original operator. This tradition has continued with other remanufactured locomotives in the CDT's Shore Line East service pool, as well as on four new GE Genesis II P32AC-DM dual-mode locomotives and six Brookville BL20GH Diesel-electric locomotives.

(from Wikipedia)